1. Field of the Invention
The present invention relates to an excitation control device for absorbing specified order harmonics superposed onto a fundamental current of an alternating current (AC) system in a synchronous machine linked to the AC system.
2. Description of the Related Art
The conventional synchronous machine excitation control device provides an excitation winding of an object synchronous machine with a direct current controlled such that the component of the fundamental current in the output voltage of the synchronous machine indicates a predetermined value.
However, the synchronous machine connected to an electric power system and controlled by the conventional excitation control device has no function of absorbing a harmonic current generated in the power system. As a result, there has been a problem of the harmonic current flowing into the synchronous machine a which current is correspondingly generated in an armature winding of the synchronous machine, thereby distorting the output voltage of the armature winding. Furthermore, a negative-phase current generated by the distortion of the system voltage flows through other apparatuses, including the synchronous machine, connected to the electric power system. This may cause various problems such as over-heating, insufficient output, etc for the apparatus.